Switch contacts



Dec. 21, 1943. D, c. LARSON SWITCH CONTACTS Filed Nov. 19, 1942 \Hlllll FIQZ INVENTOD Y E N R O T T A Patented Dec. 21, 1943 2,337,471 SWITCH CONTACTS David Carl Larson, Yonkers, N. Y., assignor to Otis Elevator Company, New York, N. Y., a cor poration of New Jersey Application November 19, 1942, Serial No. 466,212

7 Claims.

The invention relates to contacts for electric switches.

It is the practice, especially in the case of electromagnetically operated switches whose contacts are in the circuits to motors such as elevator hoisting motors, to utilize copper contacts. The copper contact is arranged to cooperate with a carbon contact in closing and opening the circuit to obviate fusing. It has been considered that iron because of certain of its properties would be totally unsuitable for electric contacts. ever, it has been found that this is erroneous and that iron is very satisfactory as a contact material, especially for contacts of the above character.

It is the object of the invention to provide a pair of switch contacts, one of whichis carbon and the principal ingredient of the other of which is iron, 1

Features and advantages of the'invention will become apparent from the following description and appended claims.

In the drawing:

Figure 1 is a somewhat simplified representation of an electromagnetic switch embodying the invention;

Figure 2 is a detail in side movable contact of the switch of Figure 1; and

Figure 3 is an end view of the same.

Referring to the drawing, the electromagneticswitch is designated l and is secu'ied to a switch panel II as by a bolt l2. The coil l3 of the switch is mounted on a switch frame I4 while the armature I5 is pivotally mounted on the end of the lower am It of the frame. The armature carries a core H which extends into the switch coil.

The movable contact l8 of the switch-sis car:

ried by the armature. the armature thus serving as a contact arm. The'stationary contact I9 is mounted on a contact stud 20 secured to the panel as by a nut 2| arranged on the threaded end of the stud. The stationary contact is in the form of a. cylinder and is of carbon or graphite. It is clamped in a contact 'holder 23 having a threaded stem 24 which extends into the con tact stud 20. The contact holderis locked in adjusted position in the stud by a nut 25. The cooperating movable contact I8 is in the form of a contact disc 21 having a. stem 28. The upper end of the contact arm is provided with an aperture 30 in which extends an insulating bushing 3|. The bushing 3| is provided with an aperture to receive the stem 28 of the contact. A spring 32 is arranged onthe bushing between a spring elevation of the I seat 33 formed on the contact arm and a flange 34 on the bushing. An insulating washer 35 is arranged on the stem on the other side of the contact arm.. A terminal clip 36 is provided on the contact stem, a washer 31 being arranged between the terminal clip and the insulating washer 35. The assembly is clamped in place by means of nuts 38 on the threaded end of the contact stem. A terminal clip 40 is also provided on the contact stud 20 and is secured thereto by an additional nut 4|.

When the armature is attracted the movable contact engages the stationary contact, the spring yielding to enable the contact arm to be pulled into full operated position. A certain amount of clearance exists for the bushing 3| in aperture 30 to enable the movable contact to properly seat itself on the stationary contact.

The disc 21 and stem 28 of the movable contact l8 are of iron. It is preferred to use malleable iron or machine steel for this contact owing to the relatively low cost of these materials and of producing a contact therefrom. Machine steel oflers certain advantages for the smaller contacts as it can be turned out of regular bar stock on a screw machine. Malleable iron castings offer certain advantages for the larger contacts, the castings being machined to form the finished contacts. pontacts formed of malleable iron castings containing in the annealed state approximately 2% carbon, 1% silicon, 3% manganese and the remainder iron except for impurities, that is containing at least 96% iron, have been found satisfactory. Also contacts formed from machine steel containing approximately 20% carbon, ;40% manganese and the remainder iron except for impurities, that is con- "Contacts which carry heavy current are madev large to insure proper heat dissipation. In the case'if iron contacts, it is found that contacts or the same size as would be used in case the contacts were copper dissipate the heat very satisfactorily. With contacts of this size the ohmic Furthermoreit has been found that the surface resistance of iron to carbon contacts is low. Iron con-= ta'cts have the further advantages that they are not readily deformable under operating conditions and that their life performance is good.

It is to be understood that the constructionor the switch shown is only illustrative and that the invention is applicable to various forms of switch? es. Also the construction of" the contact-is illustrative and other forms may be used. The

contact piece and its stem may be formed as separate units and secured together as by welding. Thercontacts may be coated with zinc or cadmium if desired for rust prevention. While malleable iron or machine steel contacts are prei'erred, it is to be understood that other grades of iron or steel may be used, including various steel alloys. Contacts formed of a chrome, nickel steel containing approximately 18 /2" chromium,

. 8% nickel, 20% carbon, .75% silicon, 50% manganese and the remainder iron, except for .impurities, that is containing at least 70% iron, haveibeen found satisfactory. What is claimed is: 1. A pair of cooperating electromagnetic switch contacts, one of which is of carbon andthe principal ingredient of the other of which is iron.

2. A pair of cooperating electromagnetic switch contacts, one of which is of carbon and the other,

of which contains at least 99% iron.

6. A pair of cooperating electromagnetic switch contacts, one of which is of carbon and theother of which is malleable iron.

'7. A pair of cooperating electromagnetic switch contacts, one of which is of carbon and the other of which is machine steel.

DAVID CARL LARSON. 

